This invention relates generally to electronic devices, and more particularly to a mask and method for forming dynamic random access memory (DRAM) contacts.
Modern electronic equipment such as televisions, telephones, radios and computers are generally constructed of solid state devices. Solid state devices are preferred in electronic equipment because they are extremely small and relatively inexpensive. Additionally, solid state devices are very reliable because they have no moving parts, but are based on the movement of charge carriers.
Solid state devices may be transistors, capacitors, resistors and other semiconductor devices. Typically, such devices are fabricated on a substrate and interconnected to form memory arrays, logic structures, timers and other components of an integrated circuit. One type of memory array is a dynamic random access memory (DRAM) in which memory cells can retain information only temporarily and must be refreshed at periodic intervals. Despite this limitation, DRAMs are widely used because they provide low cost per bit, high device density and feasibility of use.
In a DRAM, each memory cell typically includes an access transistor coupled to a storage capacitor. The memory cells are accessed by a series of word and bit lines connected to the access transistor. The word lines control the access transistors to allow the bit lines to read data into and out of the storage capacitors.
To reduce the cost of manufacturing DRAMs, multiple contact patterns have been used to form bit line contacts between a bit line and an access transistor and storage node contacts between an access transistor and a storage capacitor. Thus, separate masking processes are not needed for the bit line and storage node contacts. Multiple contact patterns, however, are typically complex due to the density and configuration of the DRAM cells. This complexity leads to difficulty in manufacturing and inspecting the patterns.
In accordance with the present invention, a mask and method for forming multiple contact patterns are provided that substantially eliminate or reduce disadvantages and problems associated with previously developed systems and methods. In particular, the present invention provides a mask and method that uses a simplified pattern to define multiple contact in a dynamic random access memory (DRAM).
In one embodiment of the present invention, a mask includes a pattern having a plurality of substantially rectangular shapes arranged longitudinally in each of a plurality of substantially parallel rows. The rows are evenly spaced apart from each other. The substantially rectangular shapes in each row are evenly spaced apart from each other and offset from substantially rectangular shapes in neighboring rows. The substantially rectangular shapes define a plurality of T-shapes connected to and offset from each other.
Technical advantages of the present invention include providing an improved mask and method for forming multiple contacts in an integrated circuit. In particular, the mask has a simplified pattern formed of a plurality of substantially rectangular shapes arranged in a plurality of rows. The substantially rectangular shapes define a plurality of T-shapes that each represent a plurality of individual contacts. The simplified pattern is not phase critical and is scalable to different geometries. Thus, complex masking features that are difficult to photo lithographically reproduce and inspect on an integrated circuit are avoided. Accordingly, manufacturing costs of the integrated circuit are reduced.
Another technical advantage of the present invention includes providing an improved mask and method for forming DRAM contacts. In particular, the mask is used to define a plurality of substantially rectangular sections to be etched from a conductive layer overlying a DRAM. Etching of the substantially rectangular sections leaves a plurality of T-shaped sections in the conductive layer that each embody a bit line contact and two storage node contacts of the DRAM. As a result, manufacturing costs of the DRAM are reduced.
Other technical advantages will be readily apparent to one skilled in the art from the following figures, description and claims.